Kim and Kourtney served up a treat for 2-for-1 Kardashian sisters in bikinis ... and Kim's ass is back to hogging the spotlight.
The Kardashians were down in Mexico this weekend with their gal pals -- including Brittny Gastineau, Malika Haqq and Larsa Pippen -- hitting the beach in some pretty revealing swimwear.
Kim's bikinis definitely took the cake ... and provided plenty too for the paps. Kourtney, meanwhile, seemed more focused on flashing some serious underboob.
Just a healthy reminder ... summer is coming.